The subject matter of the present invention relates to a recorder carrier for a drill stem testing well tool, and more particularly, to an offset recorder carrier which includes an overpressure gauge protector and a pressure balance joint in addition to a shock mount for protecting the recorders from well fluid pressures greater than a predetermined amount above the well annulus fluid pressure and for preventing the shock mount from bottoming out in response to the well fluid pressure.
Any typical drill stem testing string will include a recorder carrier for carrying pressure recorders or gauges that record the pressure of well fluids being produced from an earth formation in which the testing string is disposed. Since the drill stem testing string is adapted to be lowered into a borehole with an attached perforating gun, when the gun is detonated, a mechanical and a pressure shock is generated, the mechanical shock being transmitted up the testing string. In order to reduce this shock, a shock mount is included as part of the testing string. The pressure recorder is allowed to move up and down with respect to the recorder carrier in order to absorb and dampen the shock transmitted by the tubing string to the pressure recorder. When the shock is received by the recorders in the testing string, the recorders move uphole; however, the shock mount dampens the recorder movement and thereby prevents the recorder from being damaged as a result of the shock. If the high pressure generated due to detonation of the guns exceeds the pressure capacity of the gauge, the recorder gauges are irreversibly damaged.
Furthermore, accuracy in measurement of the well bore annulus fluid pressure is very critical. Therefore, pressure gauges that have a pressure capacity approximately equal to the well bore annulus fluid pressure are used downhole in the wellbore. Error is introduced in pressure measurements by running a high pressure capacity gauge into a low pressure well. However, during a drill stem testing operation, the tubing pressure or well fluid pressure is significantly higher than the well bore annulus fluid pressure, especially during special operations such as stimulation, internal pressure testing of tubing string, and detonation of perforating guns by pressurizing the tubing fluid. The accuracy of a pressure measurement during such special operations is not critical. An ideal situation would include using a high capacity gauge to measure well bore fluid (tubing) pressure during the above referenced special operations and a low capacity gauge to measure well bore annulus fluid pressure. However, this is not possible since all gauges are exposed at all times to the tubing (well bore) pressure. To be more specific, a pressure recorder, when mounted on the exterior of the recorder carrier, is exposed to both the well annulus fluid pressure and the well bore fluid pressure (tubing pressure). Changes of these pressures will exert either a downward or an upward force and move the recorder either up or down, respectively, in relation to the recorder carrier. The recorder will bottom out on the carrier at its upper end when the well bore fluid pressure is higher than the annulus pressure. On the other hand, the recorder will bottom out on the carrier at its downward end when the annulus pressure is higher than the well bore pressure. If the recorder bottoms out due to pressure, the shock mount becomes useless. The recorder will then be damaged due to mechanical shock even if it is shock mounted.
Furthermore, the recorder is often housed in a circumferential annular area around an inner tube of the testing string. If the outside diameter is not increased, the circumferential annular area is sometimes too small to house certain types of required pressure recorder gauges.